resource/gitlab_project_share_group: Improve documentation and reference upstream docs

Author: timofurrer

docs/resources/project_share_group.md

@@ -3,12 +3,15 @@
 page_title: "gitlab_project_share_group Resource - terraform-provider-gitlab"
 subcategory: ""
 description: |-
-  This resource allows you to share a project with a group
+  The gitlab_project_share_group resource allows to manage the lifecycle of project shared with a group.
+  Upstream API: GitLab REST API docs https://docs.gitlab.com/ee/api/projects.html#share-project-with-group
 ---
 
 # gitlab_project_share_group (Resource)
 
-This resource allows you to share a project with a group
+The `gitlab_project_share_group` resource allows to manage the lifecycle of project shared with a group.
+
+**Upstream API**: [GitLab REST API docs](https://docs.gitlab.com/ee/api/projects.html#share-project-with-group)
 
 ## Example Usage
 

internal/provider/resource_gitlab_project_share_group.go

@@ -14,7 +14,9 @@ import (
 
 var _ = registerResource("gitlab_project_share_group", func() *schema.Resource {
 	return &schema.Resource{
-		Description: "This resource allows you to share a project with a group",
+		Description: `The ` + "`" + `gitlab_project_share_group` + "`" + ` resource allows to manage the lifecycle of project shared with a group.
+
+**Upstream API**: [GitLab REST API docs](https://docs.gitlab.com/ee/api/projects.html#share-project-with-group)`,
 
 		CreateContext: resourceGitlabProjectShareGroupCreate,
 		ReadContext:   resourceGitlabProjectShareGroupRead,